Refrigeration systems are conventionally known in which a refrigerant circuit operates in a refrigeration cycle to cool and heat a room.
Patent Document 1 discloses an air conditioning system of this kind. The air conditioning system includes a refrigerant circuit in which a high-pressure stage compressor, an indoor heat exchanger, expansion valves, an outdoor heat exchanger and a low-pressure stage compressor are connected. Also connected in the refrigerant circuit are a four-way selector valve and solenoid valves, each for selecting the flow path of refrigerant. Still also connected in the refrigerant circuit is a gas-liquid separator for separating refrigerant in a gas-liquid two-phase state into liquid refrigerant and gas refrigerant.
During a heating operation of the air conditioning system, refrigerant compressed by the high-pressure stage compressor is delivered to the indoor heat exchanger. In the indoor heat exchanger, the refrigerant releases heat to room air to condense. As a result, the room space is heated. The refrigerant having condensed in the indoor heat exchanger is reduced to an intermediate pressure by a first expansion valve and then flows into the gas-liquid separator. In the gas-liquid separator, the intermediate-pressure refrigerant in a gas-liquid two-phase state is separated into liquid refrigerant and gas refrigerant. The liquid refrigerant separated in the gas-liquid separator is reduced to a low pressure by a second expansion valve and then delivered to the outdoor heat exchanger. In the outdoor heat exchanger, the refrigerant takes heat from outdoor air to evaporate. The refrigerant having evaporated in the outdoor heat exchanger is compressed by the low-pressure stage compressor and then sent to the suction side of the high-pressure stage compressor. The refrigerant is mixed with the gas refrigerant separated in the gas-liquid separator and then further compressed by the high-pressure stage compressor.
As described so far, the above refrigerant circuit operates in a so-called two-stage compression and two-stage expansion refrigeration cycle in which a two-stage expansion of reducing the pressure of high-pressure refrigerant with two expansion valves and a two-stage compression of compressing low-pressure refrigerant with two compressors are carried out and refrigerant reduced to an intermediate pressure and separated in the gas-liquid separator is sucked into the high-pressure stage compressor.
Patent Document 1: Published Japanese Patent Application No. 2001-56159